Since the discovery of ceramic high temperature superconductors in 1986, the use of these materials has been demonstrated in, the field of passive microwave components as well as in the field of so-called Josephson components. Such passive microwave components from high temperature superconductive materials are of significance, among other things, for satellite communication. Practically all uses of this type make use of epitactic thin films of high temperature superconductive as have been produced in many laboratories throughout the world. One of the important criteria for the quality of such thin films is the microwave surface resistance. It constitutes a direct measure of the microwave losses in such components.
In the art there are basically two different processes described for the determination of the microwave surface resistance of a superconductive film.
It is known according to D. E. Oates, A. C. Anderson, and P. M. Mankiewich, J. Supercond. 3, 251, 1991, for example, to produce with the aid of photolithographic techniques planar resonators from the film to be investigated. Such measuring processes are expensive and are not suitable for rapid quality control of thin films.
An alternative kind of measuring process for determining the quality of such thin films is described in A. M. Portis, D. W. Cooke, and F. R. Gray, J. Supercond. 3, 297, 1991. In this measuring process, a wall of a metallic cavity resonator is formed by the thin film to be investigated. Such process requires no pretreatment of the probe and is thus suitable for quality control. This process, however, is suitable only for frequencies above 50 GHz. A process is known further from R. C. Taber, Rev. Sci. Instrum. 61, 2200, 1990, in which two superconductive films lying upon one another form a parallel-plate resonator. It is a disadvantage, however, that the average value of the surface resistance of two films is always measured. Aside from this, the total temperature curve of the surface resistance up to the break temperature cannot be determined.